But there was one cause for celebration in Apple's earnings call: the company's spending on research and development.

As this chart from Business Insider Intelligence shows, Apple has continued to increase its R&D spend on an annualized basis even as its revenue has started to decline. This money isn't just going into new models of iPhone or iPad, either. As Tim Cook said on the earnings call, "The products that are in R&D, there is quite a bit of investment in there for products and services that are not currently shipping or derivations of what is currently shipping....You can look at the growth rate and conclude that there's a lot of stuff that we're doing beyond the current products."

Whatever Apple is building — a car, a virtual reality headset, or something nobody has reported yet — the company needs a new hit to carry Apple past the inevitable end of the iPhone era. It may not end for another decade, but nothing in tech lasts forever.